feat: add boilerplate

app/templates/join.html

@@ -0,0 +1,16 @@
+{% extends "base.html" %}
+{% block content %}
+<section class="hero pixel-panel">
+  <div class="mascot-wrap">
+    {% include "mascot.html" %}
+    <p class="speech">Session {{ session.id[:8] }} is waiting. Drop your name and jump in!</p>
+  </div>
+  {% if error %}<p class="alert">{{ error }}</p>{% endif %}
+  <form class="stack" method="post" action="/join/{{ session.id }}">
+    <label>YOUR NAME
+      <input name="name" maxlength="24" required placeholder="PLAYER 2" />
+    </label>
+    <button class="btn" type="submit">JOIN MATCH</button>
+  </form>
+</section>
+{% endblock %}